Problem: William is 5 times as old as Kevin and is also 12 years older than Kevin. How old is William?
We can use the given information to write down two equations that describe the ages of William and Kevin. Let William's current age be $w$ and Kevin's current age be $k$ $w = 5k$ $w = k + 12$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $w$ is to solve the second equation for $k$ and substitute that value into the first equation. Solving our second equation for $k$ , we get: $k = w - 12$ . Substituting this into our first equation, we get the equation: $w = 5$ $(w - 12)$ which combines the information about $w$ from both of our original equations. Simplifying the right side of this equation, we get: $w = 5w - 60$ Solving for $w$ , we get: $4 w = 60$ $w = 15$.